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Treating borers in plum tree #819401

Asked January 29, 2023, 11:59 AM EST

I have a beautiful little plum tree that has lovely spring blooms that the pollinators adore and is a very pretty shape. It does produce edible fruit but I'm really growing it as an ornamental. Birds or bugs get most of the fruit. The tree is suffering from borers, I believe. On one side of the trunk it is oozing sap from a number of places and during the growing season I saw fine wood dust in the sap. I'd love to try to save the tree. I've read about systemic insecticides that can be applied with a root drench method that may be effective. I'd do this after it flowers to limit risk to beneficial pollinators. However, I've been adding perennials around this tree to create a pollinator garden, so I don't want to use an insecticide that would harm bees if it's taken up by other plants. How much of a risk is that if I pour the mix close to the tree? Are there other methods to try to save the tree that are more bee friendly?

Wake County North Carolina

Expert Response

You have done some good research and I agree that it looks like borers have infected your plum tree.  The boring is done by the  caterpillar stage of a moth, and the research that I was able to do says that a systemic drench does not do a lot of good because of the life cycle of the moth.  The best control seems to be spraying an insecticide or maybe a larvaecide, such as Bt, on the trunk of the tree and lower branches when the larvae are active.  I’ve attached a link below to a publication that gives details on when and how to apply the spray. BTW- What I have read about systemics is that they are only taken up by roots that are actually in contact with the drench.  And thank you for taking care of the pollinators in your yard.

https://content.ces.ncsu.edu/american-plum-borer-in-ornamentals

An Ask Extension Expert Replied February 02, 2023, 5:32 PM EST

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